Movable weight-compensating suspension of the focussing objective is desired, not exclusively but above all, where treatment of living tissue is involved, and there is direct contact between the tissue and the laser system. Such direct contact is often produced, for example, in the case of operations on the human eye using laser surgery, when incisions in the cornea or other parts of the eye are to be made using ultra-short pulses of laser radiation. In this case, direct contact is intended to ensure precise positioning of the eye to be treated relative to the laser system in the direction of propagation of the radiation. Usually, a suitable interface unit (patient adapter) is connected in front of the focussing objective, and effects the physical coupling of the eye to the laser system. The interface unit usually has a holder, which is coupled to the focussing objective, for a contact element which is to be brought into contact with the eye and is made of a material which is transparent to the laser radiation. The contact element can, for example, be a plane underside for applanation of the cornea.
Focussing objectives in laser systems are often multi-lens systems, which can put considerable weight on the scales. Several kilograms are not unusual for such focussing objectives. Obviously, in an eye operation the full weight of the focussing objective must not rest on the eye being treated. Weight-compensating suspension for the focussing objective is therefore provided. The force which the focussing objective still exerts on the eye in the case of such a weight-compensating solution is reduced to a few newtons (e.g. 1 to 2 N), for example. This makes it possible to deflect the focus-sing objective upward, gently and not dangerously to the eye, if the patient suddenly happens to raise his or her head involuntarily, e.g. in a panic reaction.
An example of weight-compensating suspension of a focussing objective is given in U.S. Pat. No. 5,336,215. There the weight of the objective is compensated for by a spring system, by means of which the objective is movably suspended in a frame relative to the latter.